Process for preparing vinylidene fluoride

ABSTRACT

VINYLIDENE FLUORIDE IS PRODUCED BY THE GASEOUS PHASE REACTION OF VINYLIDENE CHLORIDE WITH AT LEAST 2 MOLS OF HYDROFLUORIC ACID PER MOL OF VINYLIDENE CHLORIDE AT A TEMPERATURE OF FROM 200* TO 400*C. IN PRESENCE OF A CATALYST SELECTED FROM TRIVALENT CHROMIUM SALTS AND ALUMINUM FLUORIDE ACTIVATED WITH A VANADIUM, TIN OR LANTHANUM COMPOUND.

3,000,450 Patented Aug. 17, T9711 3,600,450 PROCESS FOR PREPARKNG VJINYMDENE FLUURTDE Franz Kaess, 7 Adalbert tifter-Str., 8223 Traunstein, Germany; Klaus Lienhard, 11 Wiesenleite, 8223 Trostberg- Mogliug, Germany; and Horst Michaud, 6 Dr. Albert Frank-Stu, 8223 Trostberg, Germany.

No Drawing. Filed Aug. 29, 1968, Ser. No. 756,329 Claims priority, application Germany, Aug. 29, 1967, S: 111,575, S 111,576 Int. Cl. C07c 21/18 US. Cl. 260-653.3 l Claims ABSTRACT (BE THE DISCLOSURE Vinylidene fluoride is produced by the gaseous phase reaction of vinylidene chloride With at least 2 mols of hydrofluoric acid per mol of vinylidene chloride at a temperature of from 200 to 400 C. in presence of a catalyst selected from trivalent chromium salts and aluminum fluoride activated with a vanadium, tin or lanthanum compound.

This invention relates to the production of vinylidene fluoride by the fluorination of vinylidene chloride in th gaseous phase.

Vinylidene fluoride has attained considerable importance as a monomer for use in the production of homopolymers and copolymers. The homopolymers are especially useful for outside surface coatings and for chemical apparatus, because of their excellent resistance to atmospheric influences, chemicals and higher temperatures. The copolymers, especially those with trifluorochloroethylene or hexafluoropropylene, are elastomers having desirable characteristics, such as outstanding resistance to chemicals, high abrasion resistance and temperature stability.

Various methods have become known for the production of monomeric vinylidene fluoride. Processes which are based on the elimination of hydrochloric acid from 1,1,1-difluorochloroethane (German Patent No. 1,068,- 695) or hydrofluoric acid from 1,1,l-trifluoroethane (U.S. Patent No. 3,188,356) require starting materials that are difficult to obtain and relatively high temperatures, which in combination with the escaping halogen acids puts considerable demands on technology and apparatus. Moreover, such pyrolysis reactions have the disadvantage that a number of undesired by-products are often produced.

Further developments have been made due to the search for more readily available starting materials. Thus vinylidene fluoride can be produced, for example, by pyrolytic condensation of difluorochloromethane with methyl chloride (H. Mandai-R. Miller, J. prakt. Chem. 19 (4), 202, 1963). The yields according to this process, however, are relatively low and the competing reaction of the formation of tetrafluoroethylene from two molecules of difluorochloromethane is diflicult to suppress.

Vinylidene chloride is a starting material that has long been produced on a technical scale. However, previous attempts to produce vinylidene fluoride from this substance Were carried out under intermittent pressure and saturated intermediate products had then to be converted in a second step through pyrolytic halogen acid elimination into vinylidene fluoride (U.S. Patent No. 2,637,747).

The process of the present invention for the production of vinylidene fluoride comprises reacting vinylidene chloride with hydrofluoric acid in a mol ratio of 1: 2 in a single reduction step in the gaseous phase at a temperature of 200400 C. in the presence of trivalent chromium salts previously heated to the reaction temperature under non-oxidizing conditions, or in the presence of aluminum fluoride activated with vanadium, tin or lanthanum.

The trivalent chromium salts may be deposited on a support, preferably activated carbon. Chromium salts which may be used include, for example, the chloride, bromide, fluoride, sulfate, nitrate, phosphate, formate and acetate.

A chromium salt-containing catalyst for fluorination and halide exchange reactions is described in US. Patent No. 2,745,886. According to chemical analysis the catalyst has the formula CrO F In its preparation from hydrated trivalent chromium fluoride an oxidizing pretreatment is essential, so that in the resultant catalyst, chromium f higher valence is present. This patented catalyst also differs substantially in its effect from the catalyst of the p ent invention. For example, it is not possible according to the patent to substitute fluorine for halogen atoms that are directly connected to a double bond carbon atom, unless chlorine or bromine is mixed with the unsaturated halogen hydrocarbon in the reaction with hydrofluoric acid. Consequently, however, only saturated fluorine containing compounds are obtained.

It is also known from German Patent 1,000,798 to use aluminum fluoride with or without admixture with magnesium or copper or their halides as a catalyst in the production of aliphatic fluorine compounds. This method is quite satisfactory for the reaction of saturated hydrocarbons, especially in the fluorination of carbon tetrachloride. In the reaction of unsaturated halogenated hydrocarbons with hydrofluoric acid, aside from halogen substitution, hydrofluoric acid addition must also take place, so that saturated fluoridized hydrocarbons result.

With the catalysts of the present invention, a conversion to vinylidene fluoride of from to more than 99% based on the vinylidene chloride introduced in the reaction is obtained. The total non-utilizable by-products, i.e., those which cannot by return to the process be converted to vinylidene fluoride, as CH =CClF can be, amount in any case to less than 0.5% based on the vinylidene chloride introduced. In the process of the present invention, halogen exchange in the case of vinylidene chloride thus succeeds selectively, i.e., with little or no addition of hydrofluoric acid to the double bond, so that in contrast to known methods for producing vinylidene fluoride, an ad ditional step for elimination of halogen acid.is not necessary. In contrast, the results herein are unsatisfactory when aluminum fluoride is impregnated with compounds of cadmium, chromium, iron, manganese, molybdenum, nickel, zinc or zirconium.

The most favorable temperature range for the catalytic fluorination of vinylidene chloride according to the present invention is from 200 to 400 C., preferably from 250 to 350 C. At higher temperatures, the formation of by-products increases, while at lower temperatures the conversion decreases.

The reaction requires two mols of hydrofluoric acid per mol of vinylidene chloride. It has been found advantageous, however, to use in addition an excess of hydrofluoric acid. Favorably molar ratios of vinylidene chloride to hydrofluoric acid are between 1:25 and 1:6, preferably between 1:3.5 and 125.5.

The space velocity is suitably adjusted to less than 500 N ltr./h.-ltr. (500 liters gaseous reaction mixture per hour-catalyst charge volume in liters). N signifies normal conditions (pressure, temperature). The range of 100 to 300 N ltr./h.-ltr. has been found to be especially suitable.

Since the reaction proceeds Without change in mol volume, the influence of pressure is of no importance. The process is therefore suitably conducted at normal pressure, particularly since increased pressure may lead to an increased formation of by-products, especially saturated compounds.

Isolation of vinylidene fluoride from the reaction mixture and separation of the unreacted starting materials 3 is conducted in the usual manner, in such a way, however, that the latter are recovered in an anhydrous COIldltion and may be recycled into the reactor.

EXAMPLES 1 TO 7 Catalyst B: Cr(NO activated carbon containing 2.8% Cr by weight.

Catalyst C: Cr(CH COO) /activated carbon containing 2.9% Cr by weight.

In each case, 280 ml. of one of these catalysts was placed in an iron pipe reactor (27 mm. internal diameter) heated with a fused salt bath. Gaseous vinylidene chloride and hydrofluoric acid in a mol ratio of 1:4 and at a space velocity of 150 N liters of the gaseous mixture per hour-volume liter of catalyst charge were passed through the reactor at 340 C. After removing the halogen acids by washing a-nd drying, the gas mixture leaving the reactor was analyzed by gas chromatography.

The results are listed in the following table:

Yields of fiuorination products (percent) Unknown Example Catalyst CH=CF2 CH2=OFCL 011 :0012 by-products 9 A 97. 0. 7 2. 1 0. 2 10 B 97. 2 0. 6 2. 0 0. 2 11 O 98.2 0.5 1.2 0.3

perature. A mixture of vinylidene chloride (VC and EXAMPLE 12 hydrofluoric acid (HF) was then passed through. The gases emerging from the reactor were washed with water and caustic soda solution, dried and condensed in condensers cooled with liquid nitrogen. The content of vinylidene fluoride (VF in the condensate was determined by gas chromatography.

The results obtained under various working conditions are shown in the following table:

Yield of Mol Space VFa, in ratio Temp velocity mol Example VC2:HF C N ltr./h.-ltr. percent EXAMPLE 8 210 grams activated carbon with an average particle size of 2 mm. was saturated with 400 ml. of an aqueous solution of grams chromium trichloride (CrCl 6H- 0) The mixture was heated with stirring to 250 C. for

about 2 hours for the removal of the water. The catalyst D grams CrCl -6H O were dissolved in 1.5 liters of Water and trivalent chromium hydroxide wasprecipitated at elevated temperature with a small excess of ammonia, filtered, washed and divided into three parts. Each third of freshly filtered and washed chromium hydroxide was suspended in 500 ml. water and stirred with an amount just sufficient for solution of concentrated H concentrated HNO and glacial acetic acid respectively.

grams activated carbon (particle size 23 mm.) was introduced into each of three rotating tubes heated to 200-300 C. and each impregnated by adding one of the freshly prepared trivalent chromium salt solutions. In this way the following catalysts were obtained:

Catalyst A: Cr (SO activated carbon containing 2.9% Cr by Weight.

Activated Allhaving a particle size of 2-3 mm. was heated in a rotating tube to 200300 C. and during rotation, aqueous La(NO solution was dropped in. The water evaporated immediately and the lanthanum compound was deposited on the surface of the AlF particles. The catalyst formed in this way contained 3.5% by weight of lanthanum.

This catalyst was introduced into a pipe of standard steel With 27 mm. internal diameter and heated in a fused salt bath to the reaction temperature measured in the center of the catalyst layer. A gaseous mixture of vinylidene chloride and hydrofluric acid in a mol ratio 124.3 was passed through the catalyst layer at space velocity of N ltr./h.-ltr. and a temperature of 345 C. The gas mixture emerging from the reactor was passed through two receivers filled With water and 10% caustic soda solution respectively to wash out unreacted hydrofluoric acid together with hydrochloric acid resulting from the reaction. The washed gases were dried, condensed in condensers cooled with liquid nitrogen and the condensate analyzed by gas chromatography. The fluorination products were obtained in the following yields:

Percent CH =CF 96.0 CH =CFCl 0.8 Other by-products 0.2 Unreacted CH =CCl 3.0

By distillation, vinylidene fluoride of 99.9% purity and having a boiling point of 82 to 81 C. was recovered from the condensate. The compound was identified by its IR spectrum and the purity determined by gas chromatography.

EXAMPLE 13 In similar manner as in Example 12, by impregnating aluminum fluoride with an aqueous solution of ammonium vanadate, a catalyst was obtained containing 4.8% by weight vanadium.

In the apparatus described in Example 12, 1 volume part hydrofluoric acid was reacted on this catalyst with 3.5 volume parts vinylidene chloride at 330 C. The space velocity of the reaction mixture was 110 N ltr./ h.-ltr.

The reaction products obtained (in mol percent based on vinylidene chloride starting material) were Percent CH =CC1F 1.0 Other by-products 0.4 CH =CCl 4.0

EXAMPLE 14 A catalyst was prepared by impregnation of A11 with aqueous SnCl solution and contained 6.8% Sn.

A gaseous mixture of vinylidene chloride and hydrofluoric acid (mol ratio 122.9) was passed over the catalyst at 290 C. at a space velocity of 180 N ltr./h.-ltr. in the apparatus described in Example 12. From the analysis of the reaction products the following yields were calculated:

Percent CH =CClF 0.5 Other by-products (L2 CH =CCl (unreacted) 3.8

5 from the group consisting of the trivalent chromium chloride, trivalent chromium bromide, trivalent chromium fluoride, trivalent chromium sulfate, trivalent chromium nitrate, trivalent chromium phosphate, trivalent chromium formate and trivalent chromium acetate.

2. The process according to claim 1 wherein the trivalent salts are supported on activated carbon.

3. The process according to claim 1 wherein the gaseous mixture of vinylidene chloride and hydrofluoric acid is passed over the catalyst at a space velocity below 500 N ltr./h.-ltr.

4. The process according to claim 1 wherein the reaction is carried out in a continuous manner.

References Cited FOREIGN PATENTS 823,519 11/1959 Great Britain 260653.3

DANIEL D. HORWITZ, Primary Examiner US. Cl. X.R. 

